For expository convenience, the present invention is described with reference to an illustrative application thereof, namely the provision of a locked cover for mechanical locks. However, it should be recognized that the invention is not so limited. Instead, it finds application wherever access to a fixture, such as an electrical or phone outlet, a hose bib, a switch, a valve or the like, should be restricted.
Companies with mechanically-keyed doors constantly face the dilemma of whether to re-key a door or facility when a "key carrying" employee quits or is terminated. A similar issue arises when an employee loses a key. While electronic access control systems provide technical solutions to these problems, cost and installation issues associated with their implementation limit their use.
PCT publication WO 94/12749 to Hungerford shows a hybrid system in which a key to a mechanical door lock is held in a battery powered strong box adjacent the door. The strong box has a keyboard on its face. If a user correctly enters a code number on the keyboard, the strong box opens and the user can use the key contained therein to open the locked door.
While advantageous in some respects, the Hungerford system is disadvantageous in others. For example, the problem of key security still persists. If a user duplicates the key while it is out of the strong box, the element of electronic protection provided by the system is essentially defeated. The mechanical lock must be re-keyed to make the system secure again.
Further, the provision of a keypad on the outside of Hungerford's strong box invites vandalism. Keyboards are also notoriously difficult to waterproof, making the internal lock electronics susceptible to water damage. Still further, there is the recurring problem of battery failure, which can render the strong box permanently locked (or freely openable, if designed to fail in that mode). Moreover, the Hungerford system does nothing to enhance the security of the keyed lock itself; the keyed lock is still accessible to attack using conventional locksmithing tools.
In a known variant of the Hungerford system, an existing mortise lock is removed from a door and replaced with a simple flip bolt latch. A security lid is then mounted over the flip bolt. A user can only gain access to the flip bolt by entering a code on a keypad on the lid. If the code is entered properly, the lid can be opened, and the user can turn the flip bolt.
While this latter system rectifies certain of Hungerford's drawbacks, it introduces others. One is the need to remove an existing mortise lock and replace it with the flip bolt. Another, relating to physical security, is the substitution of a simple flip lock for what may have been a more robust mortise lock. Other problems of the original Hungerford system persis, including vandalism, battery failure, etc.
In accordance with a preferred embodiment of the present invention, the foregoing and other drawbacks of the prior art are overcome. An electronic security enclosure conceals a keyed lock (or other mechanical access device, such as a door knob, latch, release knob, etc.) behind a movable member. When the security enclosure is unlocked by an electronic key, and the movable member is moved to reveal the keyed lock, the key is captured, preventing its removal until the enclosure is again secured over the keyed lock. A variety of operational features, including provision for keyholder access restrictions, time-of-day restrictions, provision of different classes of keys for employees and vendors, etc., are also provided.
The foregoing and additional features and advantages of the present invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.